In-situ STM studies of the self-assembling formation of boron surface phases on Si 111/

It is well known that boron B. forms two-dimensional superstructures surface phases. if deposited on clean Si surfaces. One interesting phase is the so-called 63=63yR308 boron surface phase BSP.on Si 111.. Only a few facts are known about the step-by-step formation of this BSP and the dependence of the formation process on the degree of reconstruction of the Si surface. Therefore, we have investigated the formation of the surface phase during evaporation of B onto a Si 7=7 surface under ultra-high vacuum conditions by in-situ STM. It will be shown that the deposition of B with concentrations up to 2.6P1014 cmy2 leads to the breakdown of the 7=7 reconstructed surface and to the formation of a Si surface with a BSP located on T4lattice sites B–T4.. Thermal annealing of the structure causes the establishment of a different 63=63 reconstruction. In this second BSP, the B atoms reside in S5sites B–S5.directly underneath a Si adatom located on a T4 site. One could expect that the two phases exhibit completely different properties due to their different chemical binding. The B–T4 phase acts as a passivation layer because all of the dangling bonds of the Si surface are saturated. The B–S5 phase can be used as an atomically sharp delta-doping layer in novel electronic devices. q2000 Elsevier Science B.V. All rights reserved.